Shaping method and drum for manufacturing a tyre for vehicle wheels

ABSTRACT

A method for building a tyre for a vehicle wheel includes positioning a casing sleeve on a shaping drum and securing the sleeve on the drum. During at least one of positioning and securing the sleeve, the sleeve is kept in an essentially centered position on the drum by radial forces directed against a radially inner surface of the sleeve. A shaping drum for making a tyre for a vehicle wheel includes a rotation shaft and two coaxial half-drums integral with each other with respect to rotation. At least one of the half-drums is axially movable in both directions with respect to the other half-drum. Each half-drum includes a support device, a gripping device, and a centering device. A first equatorial plane defined the centering devices is axially movable with respect to a second equatorial plane defined by the gripping devices. A plant for building a tyre is also disclosed.

The present invention relates to a method for manufacturing a tyre forvehicle wheels, comprising the following steps: forming a casing sleeveprovided with a pair of annular bead reinforcing structures spaced apartfrom each other axially and at least one casing ply having each of itsopposite end flaps turned around one of the said annular beadreinforcing structures; transferring the casing sleeve to a shapingdrum; shaping the said casing sleeve into a toroidal configuration; andapplying a pair of sidewalls on to lateral surfaces of the casing sleeveshaped in this way, each of these surfaces extending radially outwardsfrom one of the annular bead reinforcing structures. According to theaforesaid method, the manufacture of a tyre for vehicle wheels alsocomprises the steps of forming an outer sleeve comprising a beltstructure and a tread applied in a radially external position on to thebelt structure, and transferring the said outer sleeve into a centredposition around the casing sleeve positioned on the shaping drum, tocause the outer sleeve to be applied to the casing sleeve as a result ofthis shaping. The operations associated with building the outer sleevecan be carried out in any known way and are not of any specialsignificance for the purposes of the present invention, and aretherefore not described in detail below.

The invention also relates to a building drum, and more precisely ashaping drum, for manufacturing a tyre for vehicle wheels, provided withtwo coaxial half-drums, integral with each other as regards rotation,which make up the drum, at least one of these half-drums being axiallymovable in both directions with respect to the other. Each of the saidhalf-drums comprises a suitable expandable portion which causes onesidewall to be turned so that it is applied to the corresponding lateralsurface of the casing structure; the said drum is also provided withradially expandable gripping devices for retaining the beads of thecasing sleeve on the shaping drum, and with centring devices for thecentred axial positioning of the casing sleeve on the equatorial planeof the shaping drum.

A tyre building method widely used in the art is that commonly known asthe “two-step process”. More particularly, in the tyre making processone or more casing plies are first deposited on a first cylindricaldrum, usually called the “building drum” or “first step drum”, to form acylindrical sleeve. The annular reinforcing structures at the beads arefitted on to the opposite end flaps of the casing ply or plies, whichare then turned around the annular structures in such a way as toenclose them in a kind of loop.

The casing sleeve built in this way is then transferred to a seconddrum, called the “shaping drum” or “second step drum”, on which stripsof elastomeric material for forming the sidewalls of the tyre mayalready have been positioned.

The casing is then shaped into a toroidal configuration to join it to anouter crown sleeve which has previously been placed in a centredposition with respect to the casing sleeve, and which comprises a beltstructure and a tread radially superimposed on the belt structure.

After the casing structure has been shaped, suitable expandable portionsof the shaping drum, consisting for example of lever mechanisms orinflatable chambers, cause the said strips of elastomeric material to beturned so that they are applied to the lateral surfaces of the casingstructure.

Methods and apparatus operating according to these principles aredescribed, for example, in FR-A-2,093,180 and U.S. Pat. No. 3,990,931.

The critical aspect of this method consists in the fact that all theoperations carried out in the second step are executed on a casingsleeve which may not have been perfectly centred in its fitting on theshaping drum; in other words, its equatorial plane may not coincide withthe equatorial plane of the said drum, so that it is secured on thelatter only by the securing force exerted by suitable radiallyexpandable gripping devices on the corresponding reinforcing portions ofthe casing sleeve, which will be referred to simply as “beads”, as isthe usual practice, in the following text.

This retaining force may not be sufficient to prevent smalldisplacements of the beads with respect to the corresponding grippingdevices, or the unwinding. of the casing ply from around the annularbead reinforcing structures, particularly during the step of toroidalshaping of the beads, so that, as a result of the incorrect fittingand/or subsequent displacement of the sleeve on the drum or unwinding ofthe ply at the beads, a deformed shaping of the casing is possible, andconsequently the completion of a tyre which has uneven geometry and musttherefore be discarded, since it will be unbalanced in use.

The document EP-997,263, in the context of a two-step process,illustrates a method and an apparatus for building tyres, according towhich the axial centring of the casing sleeve is ensured during itsfixing to the shaping drum at the end of the step of transferring thesleeve to the drum.

However, the problem has not been fully resolved, and has become evenmore critical with the development of a new kind of tyre, fullydescribed for example in U.S. Pat. No. 5,634,993. This tyre ischaracterized in that it has its beads, preferably with differentfitting diameters and different dimensions from each other, joined to arim having the bead support surfaces, in other words the bead bases,facing axially outwards, in other words inclined in the form of aconical surface with its vertex on the axis of rotation of the rim in aposition axially external to the tyre.

This particular bead geometry increases the risks of an incorrectcentring of the casing sleeve on the shaping drum.

The problem is further complicated by the fact that this tyre requiresthe presence of a reinforcing element on the axially inner surface ofthe bead, to protect the latter from friction against the metal surfaceof the mounting rim.

This reinforcing element is preferably assembled on to the tyre in thesecond building step, but the particular position in which it has to befixed prevents the use of centring devices acting against the axiallyinner surface of the bead, such as those described in the documentEP-997,263 cited above.

The applicant has now found that considerable advantages can beachieved, particularly in terms of reliability of the manufacturingprocesses and of the apparatus used, and in terms of the quality of thefinished product, if the casing sleeve is mounted in a position in whichit is axially and radially centred on the said drum, by means of deviceswhich enforce this centred position by bearing on inner surfaces of thesaid sleeve, thus physically preventing any displacement of the sleevefrom the predetermined position.

According to the present invention, the applicant has devised a tyrebuilding method, and also produced the corresponding shaping drum, withwhich it is possible not only to build a tyre while ensuring thestability of the axial and radial centring of the casing sleeve on thedrum during all the second-step operations, but also to assemble areinforcing element on to the axially inner surface of the bead inconjunction with the said enforced centring.

The object of the present invention is therefore a tyre building method,and the corresponding apparatus, which essentially carries out all thesteps of work on a casing sleeve which is kept axially and radiallycentred on a shaping drum.

According to another object of the present invention, the said methodand apparatus also permit the operation of assembling a reinforcing beadelement on to the axially inner surface of the said bead.

In a first aspect, the invention relates to a method for building a tyrefor vehicle wheels, comprising the steps of:

A) positioning a casing sleeve on a shaping drum; B) securing the saidcasing sleeve on the said shaping drum; C) toroidally shaping the saidcasing sleeve; D) applying a pair of sidewalls on to lateral surfaces ofthe said shaped casing sleeve; and E) applying an outer sleeve on to theradially outer surface of the said casing sleeve, in which, during theexecution of at least one of the steps C, D and E, the said casingsleeve is kept in an essentially centred position on the said shapingdrum by axial forces directed against axially inner surfaces of the saidsleeve.

During the execution of at least one of the said steps A and B, in whichthe casing sleeve is, respectively, positioned and secured on the saidshaping drum, the said casing sleeve is preferably kept in anessentially centred position on the said shaping drum by means of radialforces directed against the radially inner surface of the said sleeve.

Preferably, the aforesaid method comprises a step F) of positioning thesaid sidewalls on the said shaping drum, where the said sidewalls arepositioned with their axially inner edges in axially inner positionswith respect to the beads of the said casing sleeve.

Advantageously, the method in question comprises a further step G ofturning the said axially inner edges on to the axially inner surfaces ofthe said beads, the said step G taking place before or after the saidstep C of toroidal shaping of the said casing sleeve.

Preferably, the said step G of turning the said axially inner edges onto the axially inner surfaces of the said beads is carried out by theinflation of at least one inflatable chamber.

Alternatively, it is carried out by means of turning devices made to actagainst a radially inner surface of the said axially inner edge.

Advantageously, the said step F takes place before or after the saidstep A) of positioning the said sleeve on the said drum.

Preferably, in the method according to the invention, the said step ofpositioning the said sidewalls on the said shaping drum also comprisesthe step of securing one end of a sidewall strip on the surface of thesaid shaping drum before the said strip is wound around the said drum.

In a further aspect, the invention relates to a shaping drum for makinga tyre for vehicle wheels, starting with a casing sleeve provided withaxially opposed beads, the said drum comprising a rotation shaftconnected for operation to two coaxial half-drums, integral with eachother with respect to rotation, at least one of which is axially movablein both directions with respect to the other, each of the saidhalf-drums comprising a support device for the positioning of a sidewallon the said casing sleeve and its application thereto, a gripping devicefor securing one of the said beads on the said drum, and a centringdevice for the centred positioning of one of the said beads on the saiddrum, where the equatorial plane defined by the centring devices mountedon the said half-drums is axially movable with respect to the equatorialplane defined by the gripping devices mounted on the said half-drums.

Preferably, the said gripping device also has a first and a second guidewhich delimit a fixed path for a moving element, while the said centringdevices have a mechanism which, when operated, forces the said movingelement to move along the said fixed path, enabling the axial centringposition of the said casing sleeve to be varied with respect to theequatorial plane of the said drum.

Preferably, the said shaping drum also comprises turning devices for theassembly of the axially inner edges of the said sidewalls on to thecorresponding surface portions of the said sleeve.

Finally, the aforesaid drum preferably comprises securing devices forfixing the said sidewalls to the said drum during their positioningthereon.

Further characteristics and advantages will be made clearer by thedetailed description of a preferred, but not exclusive, embodiment of ashaping method and drum for manufacturing a tyre for vehicle wheels,according to the present invention.

This description is given below with reference to the attached drawings,provided solely for information and therefore without restrictiveintent, in which:

FIG. 1 shows schematically in partial cross section a shaping drum formanufacturing tyres according to the present invention, in the restposition, ready to receive a casing sleeve prepared elsewhere, thesidewalls of the tyre having been placed on corresponding expandableportions of the said drum;

FIG. 2 shows the drum of FIG. 1 during the fitting of the first-stepsleeve, which has now been brought to a centred position on the drum;

FIG. 3 shows the drum of FIG. 1 with elements for centring the casingsleeve in the operating position, bearing against the inner surface ofthe sleeve;

FIG. 4 shows the drum of FIG. 3 in an operating step in which, followingthe radial expansion of a gripping device of the drum, the casing sleeveis engaged at its beads;

FIG. 5 shows the shaping drum in an operating step in which, followingthe axial movement towards each other of the half-drums which make upthe drum, in conjunction with the inflation of the casing sleeve, thelatter has assumed a toroidal shape;

FIG. 6 shows the shaping drum in an operating step in which thesidewalls are applied to the axially outer lateral portions of theshaped casing sleeve;

FIG. 7 shows the shaping drum in an operating step in which reinforcingelements are applied to the axially inner lateral portions of the shapedcasing sleeve;

FIG. 8 shows the shaping drum returned to the rest position to enablethe green tyre to be removed from the aforesaid drum;

FIG. 9 shows the shaping drum in an operating step which is the same asthat of FIG. 7, but carried out according to an alternative embodiment;

FIG. 10 shows the shaping drum in an operating step which is the same asthat of FIG. 7, but carried out before the toroidal shaping of thesleeve;

FIG. 11 shows the shaping drum in an operating step which is the same asthat of FIG. 9, but carried out before the toroidal shaping of thesleeve;

FIG. 12 is a perspective view of a preferred embodiment of the mechanismof a gripping device;

FIG. 13 is a perspective view of a preferred embodiment of the mechanismof a centring device;

FIG. 14 shows, in a simplified partial longitudinal cross section, apreferred embodiment of the mechanism of the securing device;

FIG. 15 shows schematically the layout of a tyre building plantcomprising a pair of shaping drums according to the invention.

FIG. 1 shows, in partial longitudinal cross section, a drum 2 formanufacturing tyres for vehicle wheels, and, more precisely, a drumcalled a “second step” drum, in other words a drum for the toroidalshaping of a cylindrical casing sleeve built elsewhere in a differentoperating step, usually known as the first step.

The drum 2 comprises a rotation shaft 20, with one of its ends fitted ona driving motor unit 1 (FIG. 15) from which the shaft projects, themotor unit being of a known type and not relevant for the purposes ofthe present invention.

On the opposite end of the said shaft 20 there are mounted the supportelements and the operating devices which are described below and which,taken together, form one half of the said drum.

A tube 21 is fitted coaxially on the shaft 20, and is movabletelescopically between the ends of the said shaft, in other wordsmovable axially in both directions with respect to the said ends, but isintegral with the said shaft 20 with respect to rotation.

On the said tube 21 and integrally with it there are mounted deviceswhich are completely identical to and essentially mirror images of thosemounted on the shaft 20, and which are therefore not describedseparately and which are identified by the same numerical references asthose used for the devices mounted on the shaft 20; taken together, thetube and the corresponding devices form the other half of the said drum.

The drum 2 will be described with particular reference to the solutionrequired for building tyres provided with beads having different fittingdiameters, but this description is given without any restrictive intent;a person skilled in the art will easily understand how the dimensions ofthe mechanical elements of one half of the drum have to be modified toenable the drum to operate with tyres having the same fitting diameterfor both beads.

Essentially, as shown in FIG. 1, the shaping drum comprises twocoaxially aligned half-drums, movable axially with respect to eachother, but integral with each other with respect to rotation, on each ofwhich are formed tubular support devices 23 for the positioning of thesidewalls and expandable devices 30 for assembling the sidewalls on tothe casing sleeve, radially expandable gripping devices 40 for engaginga casing sleeve on the drum by the beads of the sleeve, and centringdevices 50 for positioning of the said sleeve and keeping it in acentred position on the said drum 2.

Preferably, the drum 2 also comprises turning devices 60 for assemblingthe axially inner edges of the said sidewalls on to the correspondingsurface portions of the sleeve.

Preferably, the drum 2 also comprises securing devices 70 (FIG. 14) forfixing the said sidewalls to the drum during their positioning thereon.

On the projecting end to of the said shaft 20, in other words on the endopposite the driving motor unit 1, there is mounted a tubular supportdevice 23, coaxial and integral with the said shaft, comprisingdifferent sections 23 a, 23 b and 23 c, which are connected axially toeach other but are preferably of different diameters, which decreaseaxially outwards, the radially outer surface of which is convenientlyassociated with the said radially expandable device 30 which comprisesat least one inflatable chamber 34, engaged circumferentially around thetubular support 23 and extending axially between two ends at which thechamber 34 is turned back on to itself to form a support surface for aconstituent element 81 of the tyre to be built. The said elementcomprises at least one strip 82 of elastomeric material for making asidewall of the tyre.

Preferably, there are at least two inflatable chambers 34 and 35,axially staggered with respect to each other, a second inflatablechamber 35 being provided in an axially outer and radially innerposition with respect to the chamber 34, in such a way that it is atleast partially covered by the said chamber 34.

The chambers 34 and 35 have, in a known way, suitable beads 34 a, 34 b,35 a and 35 b for securing the said chambers 34 and 35 to the radiallyouter surface of the tubular support 23 by means of suitable recessesformed in the different parts 23 a, 23 b and 23 c of said tubularsupport 23. The external surface of the tubular support 23 is preferablyshaped in such a way as to allow the chamber 34, in the rest position,to be positioned on a preferably cylindrical surface coaxial with thesaid shaft 20. Each inflatable chamber 34 and 35 can be deformed, byinjection of a pressurized hydraulic fluid, from a rest position inwhich, as shown in FIG. 1, it has an essentially cylindrical shape andis flattened against the outer surface of the tubular support 23, and anexpanded condition in which it assumes an essentially toroidal shape, asshown in FIG. 6. When the chambers 34 and 35 are inflated, the aforesaidstrip 82 of elastomeric material positioned on each of the said chambersis made to push against the lateral surface of the said shaped casingsleeve 80 (FIG. 6) to form the sidewall 81 of the tyre.

Each set of these devices is also referred to globally hereafter as theshoulder of the drum; as stated previously, the said shoulders areintegral with each other with respect to rotation and movable withrespect to each other in the axial direction between a position ofminimum spacing, when the drum is closed, and a position of maximumaxial extension, when the drum is open. It should also be pointed outthat the shoulder of the drum described here as integral with the shaft20 can also be axially movable with respect to the said shaft.

On the rotation shaft 20, in an axially inner position with respect tothe corresponding shoulder, there are radially expandable grippingdevices 40, for holding (FIG. 4) the casing sleeve 80 on the drum 2 bythe beads 83 of the sleeve.

Now that the purpose of these devices is known, a person skilled in theart will have no difficulty in designing an equivalent alternativemechanism which is more suited to his requirements and objectives.According to a preferred embodiment chosen by the applicant, the saiddevices 40 comprise (FIG. 12) a plurality of radial pins 41, distributedwith circumferential spacing between them around the rotation shaft 20.The radially inner portions of the said pins are integral with a firstguide 42 extending longitudinally along the shaft 20, which has itsradially outer surface extending axially from an axially outer end, incontact with the pin 41, of greater diameter, to an axially inner end,spaced apart from the said pin, of smaller diameter. In other words, onmoving along the radially outer surface of the said guide 42 in theaxial direction towards the outside of the drum 2, one would pass from asmaller diameter to a greater diameter; in other words one would bemoving radially outwards. This guide 42 is shown in FIG. 12 as a flangeof limited circumferential size, projecting from the said pin 41, but,preferably, the portion shown in the said FIG. 12 is part of a ringcoaxial and integral with the said shaft 20, with the radially outersurface shaped as stated, as shown in the longitudinal cross section ofFIG. 1 and in the portion in broken lines in FIG. 12.

Moving along the said guide 42 in the axial direction towards theoutside of the drum 2, there is a first portion having a markedinclination, linked to a second portion which is essentially flat andrectilinear, which, as shown in greater detail below, enables thecentring devices 50 to move axially with respect to the equatorial planedefined by the said gripping devices 40.

In a position radially external to the said first guide 42 there isprovided, integrally with the said pin 41, a second guide 43 having itsradially inner surface essentially parallel to the radially outersurface of the said first guide 42. The set of the two guides 42 and 43thus forms a fixed path for a movable element which is described below.

On the radially outer portion of the said pin 41 there is a bush 44,longitudinally slidable but fixed with respect to rotation, on which ismounted, integrally with the said bush, a shoe 45 extendinglongitudinally along the axis of the drum 2 and facing axially outwards.

The radially outer surface of the said shoe 45 is shaped in such a wayas to have a housing 45 a which can contain a ring 46 a of elastomericmaterial which is fitted around the whole plurality of shoes distributedcircumferentially around the geometric axis of the shaping drum 2.Preferably, this ring 46 a forms the axially inner bead of a flexiblemembrane 46 with two beads (46 a and 46 b) which has its axially outerbead 46 b fixed in the corresponding shoulder of the drum. The twomembranes 46, one on the shaft 20 and one on the tube 21, isolate theaxially inner portion of the drum with a fluid-tight seal in order topermit, as will be seen, the inflation and the toroidal shaping of thesleeve 80.

The aforesaid shoe 45 bears on a corresponding block 47 inserted betweenthe said shoe 45 and an operating device 48 which can be activated by atleast one fluid-dynamic actuator and which causes the shoe 45 to moveradially between a rest condition, in which it is radially withdrawnfrom the beads 83 of the sleeve, to permit the axial fitting of thecasing sleeve 80 on to the shaping drum, as shown in FIG. 2, and theremoval of the tyre on completion of the building process, as shown inFIG. 8, and an operating condition, in which, as shown in FIGS. 4 to 7,it pushes against the beads 83 of the aforesaid sleeve.

Preferably, the said fluid-dynamic actuator comprises a piston 49coupled to the aforesaid device 48 along a conical surface coaxial withthe drum 2 and facing axially outwards, with its vertex on the axis ofrotation of the drum in an axially inner position; as a result of thiscoupling, a longitudinal movement of the piston 49 axially towards theinterior of the drum causes the radial outward movement of the block 47and of the shoe 45 associated with it. The returning radially inwardmovement of the shoe 45 can be provided by the elastic ring 46 a, whichhas expanded during the radial expansion of the shoes. Additionaldevices (not illustrated) can be provided alternatively orsimultaneously to facilitate or produce this return movement, such asdovetail joints between the corresponding conical surfaces of the block47 and the device 48, or springs acting directly on the block and/or onthe said device.

The device 48 is shown in FIG. 12 as a strut of limited circumferentialsize, but, preferably, the portion shown in the said figure is part of aring coaxial with the said shaft 20, with its radially outer surfaceconical as stated above, as shown in the longitudinal cross section ofFIG. 1 and in the portion in broken lines in FIG. 12.

The said ring 48 is axially slidable within a cylinder 26 keyed on therotation shaft 20 and closed at its axially outer end; an operatingfluid is injected into the said cylinder 26, between the closed end andthe axially outer surface of the piston 49, causing the axial movementof the said piston. Suitable sealing rings prevent the leakage of thefluid out of the cylinder 26 along the radially outer surface of thepiston 49.

According to the invention, the drum 2 can be provided with turningdevices 60 for assembling the axially inner edges of the said sidewalls81 on to the corresponding surface portions of the sleeve 80.

Now that the purpose of these devices is known, a person skilled in theart will have no difficulty in designing an equivalent alternativemechanism which is more suited to his requirements and objectives. In apreferred embodiment (FIG. 12), these devices 60 comprise, again withreference to only one of them, a flange 61 integral with the bush 44,extending axially from the said bush towards the interior of the drum.

On the said flange 61 there is pivoted, with an axis of rotationperpendicular to the plane of the longitudinal cross section of thedrum, a lever 62 which has its axially outer end resting on the radiallyinner end of the said bush 44; preferably, its axially inner end isprovided with a tooth 63 extending radially outwards.

It will be easily understood that a force applied to the tooth 63, or tothe corresponding end of the lever 61, in a radially inward direction,will make the lever rotate about its axis of rotation, thus raising itsaxially outer end in a radially outward direction.

Also according to the invention, the drum 2 additionally comprisescentring devices 50 (FIG. 13) for the positioning of the said sleeve 80on the said drum and for keeping it in a centred position. Now that thepurpose of these devices is known, a person skilled in the art will haveno difficulty in designing an equivalent alternative mechanism which ismore suited to his requirements and objectives. In a preferredembodiment, the said devices 50 comprise a ring 51, coaxial with thedrum 2 and axially slidable on the said shaft 20, carrying on itsradially outer surface a plurality of cylinders 52, extending radiallyoutwards and distributed circumferentially with spacing between them.FIG. 13 shows only one of the said cylinders 52, mounted on a limitedcircumferential portion of the said ring 51, which for the sake ofsimplicity is shown as being straight.

Within the said cylinder 52 there is a radially slidable piston 53 whichcarries on its radially outer end an element (centring piece) 54positioned parallel to the axis of the drum 2 and extendinglongitudinally outwards.

The radially inner end of the said piston 53 is integral with one end ofa pin 55, which is perpendicular to the radial plane containing the axisof the piston 53 and the axis of rotation of the drum, and which isslidable within a longitudinal recess 56 formed in the lateral wall ofthe cylinder 52. This pin 55 carries on its opposite end a roller 57which rotates freely with respect to the axis of the said pin 55. Thediameter of the said roller 57 is essentially equal to the aperture, inother words the radial dimension, of the aforesaid fixed path formedbetween the said first and second guides 42 and 43. In particular, thering 51 is mounted on the shaft 20 with an angular orientation withrespect to the gripping devices 40, in such a way that the cylinders 52of the centring device 50 are positioned alternately with the pins 41 ofthe gripping device 40, with the rollers 57 on the aforesaid fixed path.At least one operating device, but preferably at least two devices,located with equal circumferential spacing between them, move theaforesaid ring 51 axially. Preferably, the said operating devicecomprises a fluid-dynamic actuator of the cylinder and piston type, withthe cylinder 58 integral with the shaft 20 and the piston 59 integralwith the ring 51.

The operation of the mechanism is evident: the movement of the ring 51towards the end of the drum moves the piston 53 in an axial directionand forces the roller 57 to move along the fixed path on the radiallyouter surface of the guide ring 43, thus causing a simultaneous radialoutward movement of the said piston 53 and of the centring piece 54connected to it.

It should be noted that, when the piston 59 is operated, the movement ofthe roller 57 within the said fixed path, which as stated previouslyincludes a straight portion because of the shaping of the first guide42, will cause an axial movement of the centring devices 50, andconsequently of the equatorial plane defined by them, with respect tothe equatorial plane defined by the gripping devices 40 mounted on thesaid half-drums of the shaping drum 2.

Known devices (not illustrated), preferably of the elastic type, areprovided to vary the length of the piston 53 in such a way that the saidcentring device 50 can be used with casing sleeves having diameterslying within a predetermined range of values. For example, a simple andadvantageous embodiment of the said elastic devices comprises acompression spring fitted between a radially inner portion and aradially outer portion of the said portion 53, which is convenientlymade in telescopic form.

It should be noted that the type of mechanism provided for the centringdevice 50 (with actuators 58 and 59 provided on both shoulders of thedrum) makes the positioning of the centring pieces 54 independent of theaxial position of the shoes 45; thus it becomes possible to vary theaxial centring position of the sleeve with respect to the equatorialplane of the drum which is equidistant from the axially opposed shoes45, with the advantages described below.

Preferably, the drum also comprises securing devices 70 for fixing theelastomeric strips 82 to the surface of the drum 2 during theirpositioning on the shoulders of the said drum. The said securing devices70 preferably comprise at least one clamping member 71 movable radiallyand axially with respect to the shaping drum 2, provided on each half ofthe drum. More particularly, the clamping member 71 (FIG. 14) is movablebetween a rest position, in which it is disengaged from the edge of thestrip 82 and positioned on the shaping drum 2 in such a way as to forman axially inner shoulder with respect to the axially outer edge of thebead ring 46 a of the chamber 46, and an operating position, in which itforms an axially outer shoulder with respect to the axially inner edgeof the said bead ring 46 a and acts on a edge of the corresponding strip82 of elastomeric material supplied from a sidewall feed unit 3 (FIG.15) to secure it on the outer surface of the shaping drum. This clampingmember 71 moves in space and time independently of the movements of theother gripping devices 40 and centring devices 50. Where its mechanismis concerned, preferably this is entirely identical to that of thecentring devices 50, or alternatively to that of the gripping devices40, and therefore its description is not repeated here: it is simplypointed out that, unlike the centring devices 50, the clamping members71, when operated, have to move radially inwards to secure the saidstrips 82, and not radially outwards. It should also be noted that thedrum has only one pair of axially opposed clamping members 71, while thecentring devices 50 are circumferentially distributed over the wholeperimetric extension of the drum. In any case, now that the purpose ofthese clamping members 71 is known, a person skilled in the art willhave no difficulty in designing an equivalent alternative mechanismwhich is more suited to his requirements and objectives.

It is also clear that, in order to simplify the architecture of thedrum, the said clamping members 71 can be replaced by equivalent deviceswhich are external to the drum and do not form part of it.

The drum 2 described above is designed for the execution of theoperations which, in a two-step building process, lead to the completionof tyre casings, prepared in the form of cylindrical sleeves 80 during afirst step of the said process.

A tyre for vehicle wheels is, in general terms, a known structure whichdoes not require detailed description here. It essentially comprises acasing sleeve 80 (see FIG. 2) reinforced with at least one casing plywhich has circumferential axially opposed flaps turned in a loop aroundcorresponding annular reinforcing structures which, in the finishedtyre, are embedded in the areas usually known as “beads” 83, located inthe inner circumferential edges of the tyre. As shown in FIG. 2, eachannular reinforcing structure comprises at least one circumferentiallyinextensible annular insert 84, usually called the “bead wire”, and anelastomeric filler 85 applied in a position radially external to thebead wire.

The casing sleeve 80 is associated, in a radially outer position, duringa step E), with an outer sleeve having a belt structure usuallycomprising one or more belt strips. A tread designed to provide thecontact surface of the tyre with the running surface is applied in aposition radially external to the belt structure.

On the lateral surfaces of the casing structure 80, each extendingradially from one of the beads 83 to the crown portion of the casing 80,there are applied corresponding sidewalls 81 of elastomeric material. Intyres requiring a reinforcing element in a position axially inside thebead 83, such as the tyre of a new type mentioned above, the saidreinforcing element preferably consists of a sheet 86 of elastomericmaterial, having suitable rheometric characteristics, which may alsoinclude a fibre, textile or metallic reinforcement pre-assembled on tothe strip of elastomeric material of the sidewall 81 on its edge facingthe bead 83. In the remainder of the present description, the term“sidewall” will be frequently and exclusively used, for the sake ofsimplicity, even when the sidewall comprises the aforesaid reinforcingsheet.

In the toroidally shaped casing, each sidewall conveniently has aradially inner terminal edge which can extend axially from the outsideto the inside around the corresponding annular reinforcing structure 84,and a radially outer terminal edge which can be laterally superimposedon the corresponding lateral edge of the tread, to form a structuralsystem of the type usually called “sidewalls over”, or can be interposedbetween the casing structure and the lateral edge of the tread, in astructural system of the type called “sidewalls under”.

This casing structure is initially prepared, in any way convenient tothe person skilled in the art, in the form of a cylindrical sleeve,usually called the “casing sleeve” 80, incorporating the annularreinforcing structures in the beads facing radially towards thegeometric axis of the sleeve, as in FIG. 2.

In particular, the attached figures show a casing sleeve provided withbeads having different fitting diameters, but this is done solely inorder to provide greater detail and without any restrictive intent,since the invention is applicable to any type of tyre.

The casing sleeve prepared in this way is now ready to be transferred tothe shaping drum 2 according to the invention. It should be pointed outhere that the drum according to the invention can also be used formounting the casing sleeve in an off-centre position with respect to theequatorial plane of the drum; in this case also, for simplicity, theterm “centred position” will continue to be used in the course of thepresent description.

Before the casing sleeve 80 is transferred to the said drum 2, and ifthe sleeve has not already been provided with sidewalls 81 assembled onto it during the first-step operation, the sidewalls are positioned onthe shaping drum. This operation can be carried out even after thecasing sleeve 80 has been secured on the gripping device 40 of theshaping drum, but, in this case, it will no longer be possible to laydown a sidewall having an inner terminal edge to be turned around thecorresponding annular reinforcing structure, since the sidewall can belaid down only in a position axially external to the aforesaid annularreinforcing structure. The operation is preferably carried out byfeeding on to each of the half-drums of the shaping drum at least onestrip of elastomeric material designed to form one of the sidewalls.More particularly, the strip can be, for example, drawn from a feed reelor other continuous supply device, and guided towards a correspondingapplication area positioned tangentially with respect to the shapingdrum, as shown in FIG. 15, this being done in a known way.

The operating sequence for the purposes of a step F) for positioning thesidewalls essentially requires the shaping drum to be rotated angularlyuntil the clamping members 71 are brought close to the ends of thestrips of elastomeric material which have been positioned in theapplication area by means of guide elements. In this step, the clampingmembers 71 are moved axially and radially until they are brought intothe operating position in which they engage the ends of the strips ofelastomeric material in the corresponding application areas of theshaping drum. The shaping drum is then rotated to wind on a completeturn of the strips of elastomeric material, drawn from the aforesaidsupply devices 3. Simultaneously with the said winding, the strips ofelastomeric material are cut to size by suitable cutting membersassociated with the said guide elements, in such a way that the oppositeends of each length which is produced come into contact with each otherto form a joint, preferably of the chamfer type, on the shaping drum.The final joint between the ends can be formed manually by an operatoror by means of suitable devices, for example known roller devices whichare not illustrated. On completion of the winding, the clamping members71 are returned to the rest position and each of the sidewalls, as shownin FIG. 1, is essentially shaped in the form of a cylindrical ring witha cross-sectional profile extending axially with respect to the shapingdrum. Preferably, the axially inner terminal edge of each sidewall isalso made to be at least partially superimposed on the bead ring 46 a ofthe gripping device 40 provided on the shaping drum for engagement withthe casing sleeve 80.

The casing sleeve 80, removed from the building drum 4 (FIG. 15) by theradial contraction of the latter, is transferred (FIG. 2) on to theshaping drum 2 according to the invention, by means of a transfer device5 (FIG. 15), which is not illustrated in detail since it is known and isnot relevant. On reaching the shaping drum 2, the said casing sleeve 80is positioned or fitted on it during a step A).

The centring devices 50 (FIG. 2) are then operated, and these, by anaxially and radially outward movement, come to bear on the inner surfaceof the casing sleeve 80, in the area of the beads 83, thus causing theaforesaid sleeve, at least during a step B in which the sleeve issecured to the drum, to take up a position which is radially centredwith respect to the axis of rotation of the drum and axially centredwith respect to a reference plane usually consisting of the equatorialplane of the drum 2.

However, it should be noted that the said equatorial plane of theshaping drum 2, in other words that defined by the gripping devices 40,can be different from the equatorial plane defined by the aforesaidcentring devices 50, in other words from the equatorial plane of thecasing sleeve 80. This possibility of changing the position of thecasing sleeve along the shaft 20 is due, as stated above, to the factthat the position of the ring 51 with respect to the pin 41 is variable,within certain limits, independently of each half of the drum.

After the sleeve has been brought into a centred position with respectto the drum, the actuators are brought into operation to radially expandthe shoes 45 of the gripping devices 40 (FIG. 4), thus bringing theminto the corresponding operating position, to hold the casing sleeve 80by the annular reinforcing structures 84.

In this step, carried out with the centring devices 50 still in theoperating position, as shown in the said figure, the sidewall 81 isadvantageously secured on to the radially inner surface of the bead 83of the sleeve, thus ensuring the correct axial positioning of the endsof the sidewall with respect to the casing sleeve and the stability ofthe said positioning of the sidewall during the subsequent steps of theprocess.

The toroidal shaping of the sleeve 80 is then carried out by means of astep C). This operation is carried out by causing the componenthalf-drums of the shaping drum 2 to approach each other axially, whilesimultaneously injecting an operating fluid into the casing sleeve 80,in such a way as to make it expand radially in a toroidal configuration.In this step, the casing sleeve is compelled to remain centred on thedrum by the action of the centring devices 50 which continue to be keptin the operating position. The action of these devices against theannular reinforcing structures 84 also prevents any possibility of theunwinding of the casing ply around the bead wires.

The radially expandable devices 30 associated with the shoulders of theshaping drum 2 are then brought into action to cause, in a step D), theapplication of each sidewall 81 on to a corresponding lateral surface ofthe casing sleeve 80. In the preferred solution described initially,these devices 30 essentially comprise the pair of inflatable chambers 34and 35 around which the strips 82 of elastomeric material, designed toform the sidewalls 81, have been wound.

Preferably, the sequence of operation of the inflatable chambers 34 and35 is such that the first chambers 34 located in the axially innerposition are initially inflated, to raise the sidewall 81 with respectto the outer surface of the shaping drum 2 and to turn up the saidsidewall towards the lateral surface of the casing sleeve 80. The secondchambers 35 are subsequently operated, to complete the application ofthe sidewalls and compress them against the casing sleeve.

The chambers 34 and 35 are then deflated and returned to their restposition; a rolling operation is then carried out to compact thesidewall strips against the sides of the casing.

In a known way, during the shaping operation or at any subsequentmoment, before or after the application of the sidewalls, the sleeve 80is also joined to the outer sleeve which carries the belt structure andthe tread. This operation is also followed by a rolling of the saidouter sleeve against the shaped casing sleeve.

During these steps, the centring devices 50 provide a forced axialcentring of the casing sleeve, thus preventing any possible displacementof the sleeve from its centred position which might otherwise occur as aresult of the forces generated by the rolling operation.

When required, a step G of turning the axially inner edge of thesidewall 81 on to the axially inner surface of the bead 83, in aposition radially inside the casing 80, is then executed. The operationis carried out by returning the centring devices 50 to the restposition: in this step, during the radial inward movement, each end of acentring device presses radially inwards against the correspondingaxially inner end of the lever of the turning device 60, causing itsaxially outer end to rotate about the pivot and consequently to moveradially outwards. This movement moves the end of the inflatable chamberradially outwards, causing the inner edge of each sidewall 81 to beapplied on to the surface of the sleeve.

At this point, the gripping devices 40 of the shaping drum 2 are alsoreturned to the rest position to enable the built tyre to be removed.

Alternatively, as shown in FIG. 9, if the drum 2 is not provided withthe aforesaid turning devices 60, the aforesaid turning operation can becarried out by inflating the axially inner terminal portion of theinflatable chamber 34, the said portion extending axially towards theinterior of the said drum 2 until it passes beyond the axially inner endof the bead ring 46 a, and being provided with its own inflation valvewhich enables the said axially inner terminal portion to be operatedseparately from the remaining portion of the chamber.

In another alternative variant of the method according to the invention,the step of turning the axially inner portion of the sidewall on to theaxially inner surface of the bead is carried out before the toroidalshaping of the sleeve; in this case also, it can be carried out by meansof the aforesaid turning devices 60, operated as stated.

In this case, as an alternative to the described process, the turningdevices 60 can be used as elements for maintaining the centring of thecasing sleeve 80 during the application of the outer belt sleeve.

Alternatively (FIG. 11), in the absence of the aforesaid turning devices60, the turning can be carried out by separately inflating the axiallyinner terminal portion of the inflatable chamber 34.

In this alternative variant embodiment, the centring devices, removed toallow the said step of turning the axially inner portion of thesidewall, are returned to the sleeve centring position before thetoroidal shaping of the sleeve is carried out.

Alternatively, it is possible, as stated, to use the turning devices 60kept in the centring position.

The shaping drum 2 according to the invention can advantageously be usedin a complete plant for building tyres by the two-step method. Inparticular, FIG. 15 shows a tyre building plant which has a first-stepbuilding drum 4, a device 5 for transferring the first-step sleeve 80,an auxiliary drum 8 for building the outer sleeve comprising the beltstructure and tread, a device 7 for transferring the said outer sleeve,and at least one shaping drum 2 according to the present invention,supported by and projecting from a motor unit 1 mounted on a rotatableturret 6 designed to change the relative positioning of the said shapingdrum 2, preferably by rotations of 180° about a vertical axis, between aposition 2 a for receiving the casing sleeve 80 and a position 2 b forreceiving the outer sleeve with the belt and tread.

Preferably, there is a pair of shaping drums 2 supported by andprojecting from opposite sides of the said motor unit 1, in the saidpositions 2 a and 2 b respectively.

Advantageously, the use of two shaping drums in place of a single drumenables the operating cycle to be reduced, thus increasing the output ofthe plant accordingly.

At the position 2 a of the shaping drum in which it is coaxial with thedrum 4, there is also a feed device 3 for supplying the sidewall strips,and other semi-finished products which may be required, to the saidshaping drum 2.

The present invention yields significant benefits.

As a result of the present invention, an absolutely precise initialcentring of the sleeve on the shaping drum is achieved, even when thebeads of the sleeve have different fitting diameters, which might causethe positioning of the equatorial plane of the sleeve not to beperpendicular to the axis of rotation of the drum.

The independence of the axial movement of the centring devices 50 withrespect to the gripping devices 40 enables the casing ply of the sleeve80 to be placed in tension in a cylindrical configuration independentlyof the width of the aforesaid sleeve, thus enabling the same shapingdrum to be used for different grades of tyre.

Furthermore, the centring, particularly the axial centring, of thesleeve on the drum is ensured throughout all the tyre buildingoperations, many of which require the application of considerable forcesto the sleeve, particularly in the axial direction.

Additionally, the operation of turning the axially inner edges of thesidewalls in an axially inner position with respect to the beads ispermitted, or in any case considerably simplified, whereas thisoperation is difficult to carry out in the known processes and with the-known building drums; the correct radial positioning of the edges ofthe sidewall on the casing sleeve is also ensured.

It should also be noted that the possibility of varying the axial pathof the centring devices 50 with respect to the corresponding grippingdevices 40 provides at least two further advantages. Firstly, itsimplifies the sidewall feed system and facilitates the change of grade,since it allows the sidewalls to be deposited on the drum in the samerelative axial position at all times, independently of the width of thefirst-step sleeve, thus making it unnecessary to adjust the feed unit 3(FIG. 15) to allow for this width.

Secondly, the axial movement of the gripping device 40 with respect tothe centring device 50, made possible by the drum according to theinvention, enables the sidewalls to be deposited on the drum even afterthe sleeve has been received and centred with respect to the drum, inthe absence of any interference between the said two devices: inparticular, it enables a sidewall strip to be wound on to the saidgripping device 40 so that it can subsequently be secured between thegripping device and the corresponding bead of the sleeve, the axiallyinner terminal edge of the said strip being thus fixed in an axiallyinner position with respect to the said bead.

1-21. (canceled) 22: A method for building a tyre for a vehicle wheel,comprising: positioning a casing sleeve on a shaping drum; securing thecasing sleeve on the shaping drum; toroidally shaping the casing sleeve;applying a pair of sidewalls to lateral surfaces of the shaped casingsleeve; and applying an outer sleeve to a radially outer surface of thecasing sleeve; wherein during at least one of toroidally shaping thecasing sleeve, applying the pair of sidewalls, and applying the outersleeve, the casing sleeve is kept in an essentially centered position onthe shaping drum by axial forces directed against axially inner surfacesof the casing sleeve, and wherein during at least one of positioning thecasing sleeve and securing the casing sleeve, the casing sleeve is keptin an essentially centered position on the shaping drum by radial forcesdirected against a radially inner surface of the casing sleeve. 23: Themethod of claim 22, further comprising: positioning the sidewalls on theshaping drum; wherein the sidewalls are positioned with axially inneredges of the sidewalls in axially inner positions with respect to beadsof the casing sleeve. 24: The method of claim 23, further comprising:turning the axially inner edges of the sidewalls onto axially innersurfaces of the beads. 25: The method of claim 24, wherein turning theaxially inner edges takes place before toroidally shaping the casingsleeve. 26: The method of claim 24, wherein turning the axially inneredges takes place after toroidally shaping the casing sleeve. 27: Themethod of claim 24, wherein turning the axially inner edges is carriedout by inflating at least one inflatable chamber. 28: The method ofclaim 24, wherein turning the axially inner edges is carried out usingturning devices made to act against radially inner surfaces of theaxially inner edges. 29: The method of claim 28, wherein the turningdevices are used as elements for maintaining the essentially centeredposition of the casing sleeve during applying the outer sleeve. 30: Themethod of claim 23, wherein positioning the sidewalls takes place beforepositioning the casing sleeve. 31: The method of claim 23, whereinpositioning the sidewalls takes place after positioning the casingsleeve. 32: The method of claim 23, wherein for each sidewall,positioning the sidewalls comprises: securing one end of a sidewallstrip on a surface of the shaping drum before the strip is wound aroundthe shaping drum. 33: A shaping drum for making a tyre for a vehiclewheel, comprising: a rotation shaft; and two coaxial half-drums; whereinthe rotation shaft is connected for operation to the half-drums, whereinthe half-drums are integral with each other with respect to rotation,wherein at least one of the half-drums is axially movable in bothdirections with respect to the other half-drum, wherein each half-drumcomprises: a support device; a gripping device; and a centering device;wherein the support device positions and applies a sidewall on a casingsleeve, wherein the gripping device secures one axially opposed bead ofthe casing sleeve on the half-drum, wherein the centering devicepositions one of the axially opposed beads on the half-drum, and whereina first equatorial plane defined by the centering devices is axiallymovable with respect to a second equatorial plane defined by thegripping devices. 34: The shaping drum of claim 33, wherein the grippingdevices comprise first and second guides that delimit a fixed path for amoving element. 35: The shaping drum of claim 34, wherein the centeringdevices comprise a mechanism that, when operated, forces the movingelement to move along the fixed path, thus varying the axial centeringposition of the casing sleeve with respect to the equatorial plane ofthe shaping drum. 36: The shaping drum of claim 33, further comprising:turning devices for assembling the axially inner edges of the sidewallsonto corresponding surface portions of the casing sleeve. 37: Theshaping drum of claim 33, further comprising securing devices forsecuring the sidewalls to the shaping drum during winding of sidewallstrips onto the shaping drum. 38: A method for building a tyre for avehicle wheel, comprising: positioning a casing sleeve on a shapingdrum; and securing the casing sleeve on the shaping drum; wherein duringat least one of positioning the casing sleeve and securing the casingsleeve, the casing sleeve is kept in an essentially centered position onthe shaping drum by radial forces directed against a radially innersurface of the casing sleeve. 39: A method for building a tyre for avehicle wheel, comprising: positioning a casing sleeve on a shapingdrum; securing the casing sleeve on the shaping drum; positioning a pairof sidewalls on the shaping drum; and turning axially inner edges of thesidewalls onto axially inner surfaces of beads of the casing sleeve;wherein the sidewalls are positioned with the axially inner edges of thesidewalls in axially inner positions with respect to the beads of thecasing sleeve. 40: A method for building a tyre for a vehicle wheel,comprising: positioning a casing sleeve on a shaping drum; and securingthe casing sleeve on the shaping drum; wherein the shaping drumcomprises centering devices for the casing sleeve, wherein the shapingdrum comprises gripping devices for the casing sleeve, wherein thecasing sleeve is secured on the shaping drum using the gripping devices,wherein the casing sleeve is secured on the shaping drum with anequatorial plane of the casing sleeve being different from an equatorialplane of the shaping drum, wherein the equatorial plane of the casingsleeve is defined by a position of the centering devices, and whereinthe equatorial plane of the shaping drum is defined by the grippingdevices. 41: A plant for building a tyre for a vehicle wheel,comprising: a first-step building drum; a device for transferring afirst-step sleeve; at least one shaping drum; an auxiliary drum forbuilding an outer sleeve; a device for transferring the outer sleeve;and a feed device provided next to the at least one shaping drum;wherein the at least one shaping drum is supported by a motor unit,wherein the at least one shaping drum projects from one side of themotor unit, wherein the outer sleeve comprises: a belt structure; and atread; wherein the feed device is coaxial with the building drum,wherein the at least one shaping drum comprises: a rotation shaft; andtwo coaxial half-drums; wherein the rotation shaft is connected foroperation to the half-drums, wherein the half-drums are integral witheach other with respect to rotation, wherein at least one of thehalf-drums is axially movable in both directions with respect to theother half-drum, wherein each half-drum comprises: a support device; agripping device; and a centering device; wherein the support devicepositions and applies a sidewall on the first-step sleeve, wherein thegripping device secures one axially opposed bead of the first-stepsleeve on the half-drum, wherein the centering device positions one ofthe axially opposed beads on the half-drum, and wherein a firstequatorial plane defined by the centering devices is axially movablewith respect to a second equatorial plane defined by the grippingdevices. 42: The plant of claim 41, further comprising: a pair ofshaping drums; wherein the pair of shaping drums are supported by themotor unit, wherein the pair of shaping drums project from oppositesides of the motor unit, and wherein the motor unit is mounted on arotatable turret designed to change positioning of the pair of shapingdrums with respect to each other.